So, with direct-to-AirTunes support presumably in the near future, I think this discussion needs a bump. An obvious extension of the whole web based library navigator/playlist creator is the ability to push it to a given AirTunes client.
I was just exploring the Playlist page, and I see that it does load my playlist (took a few minutes, 18,000+ songs), but the genre/artist/album sections collapse as soon as I click in them. I’m using ff on mac os x tiger.
All in all though, one of my favorite pieces of software.